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| United States Patent |
5,231,134
|
|
Carpenter
, et al.
|
July 27, 1993
|
Process for the preparation of an amine modified copolymer as a pigment
dispersant for cathodic electrocoating compositions
Abstract
The present invention is directed to a process for the preparation of amine
modified copolymers as a pigment dispersant for cathodic electrocoating
compositions comprising the steps of
a) polymerizing
i) an ethylenically unsaturated monomer containing an isocyanate group with
ii) other ethylenically unsaturated monomers having no functional group
capable of undergoing a reaction with said isocyanate group to form a
copolymer with isocyanate groups and
b) reacting stepwise or simultaneously said isocyanate groups with
iii) a compound selected from the group consisting of a polyalkyleneglycol
monoalkyl ether, an aminoterminated polyalkylene glycol monoalkyl ether
and mixtures thereof and
iv) a compound containing at least a tertiary amine group and one
functional group capable of undergoing a reaction with said isocyanate
group and
v) optionally, another compound having one functional group capable of
undergoing a reaction with said isocyanate group.
| Inventors:
|
Carpenter; Clint W. (Royal Oak, MI);
Steinmetz; Alan L. (Milford, MI)
|
| Assignee:
|
BASF Corporation (Parsippany, NJ)
|
| Appl. No.:
|
751025 |
| Filed:
|
August 29, 1991 |
| Current U.S. Class: |
525/123; 525/125; 525/126; 525/127; 525/187; 525/328.2 |
| Intern'l Class: |
C08F 008/30; C08L 075/00 |
| Field of Search: |
525/123,125,126,127
|
References Cited
U.S. Patent Documents
| 4565852 | Jan., 1986 | Qaderi | 525/528.
|
| 4624762 | Nov., 1986 | Abbey et al. | 524/507.
|
Primary Examiner: Kight, III; John
Assistant Examiner: Truong; Dve
Attorney, Agent or Firm: Werner; Frank G., Marshall; Paul L.
Claims
We claim:
1. A process for the preparation of amine modified copolymers as pigment
dispersants for cathodic electrocoating compositions comprising the steps
of
a) polymerizing
i) an ethylenically unsaturated monomer containing an isocyanate group with
ii) other ethylenically unsaturated monomers having no functional group
capable of undergoing a reaction with said isocyanate group to form a
copolymer with isocyanate groups and
b) reacting stepwise or simultaneously said isocyanate groups with
iii) a compound selected from the group consisting of a polyalkyleneglycol
monoalkyl ether, an aminoterminated polyalkylene glycol monoalkyl ether
and mixtures thereof and
iv) a compound containing at least a tertiary amino group and one
functional group capable of undergoing a reaction with said isocyanate
group and
v) optionally, another compound having one functional group capable of
undergoing a reaction with said isocyanate group.
2. A process according to claim 1, wherein in step (a) are used about 5 to
about 50% by weight (i) and about 50 to about 95% by weight (ii).
3. A process according to claim 1, wherein the monomer (i) is selected from
the group consisting of dimethyl-meta-isopropenyl benzyl isocyanate,
vinylisocyanate, isocyanatoethyl(meth)acrylate, isopropenyl isocyanate and
mixtures thereof.
4. A process according to claim 1, wherein the monomer (ii) is selected
from the group consisting of acrylic or methacrylic alkyl, aryl, aralkyl,
alkoxyalkyl or aryloxyalkyl esters derived from alcohols or phenols having
to about 20 carbon atoms, or vinyl monomers and mixtures thereof.
5. Amine modified copolymers obtainable by the process according to claim
1.
6. An aqueous pigment dispersion comprising an amine modified copolymer
according to claim 1.
7. An aqueous coating composition comprising an amine modified copolymer
according to claim 1.
8. An article coated with an aqueous coating composition according to claim
7.
Description
FIELD OF THE INVENTION
The present invention is directed to a process for the preparation of an
amine modified copolymer, more specifically it is directed to an amine
modified copolymer as a pigment dispersant for a cathodic electrocoating
composition.
BACKGROUND OF THE INVENTION
Cathodic electrodeposition as a coating application method for metallic
substrates is well known and described for example in U.S. Pat. Nos.
4,575,523; 4,661,541; 4,780,524 and 4,920,162.
The electrocoating composition comprises a principal resin, a crosslinker,
a grind resin, pigments and other additives such as solvents, control
agents, fillers and the like.
Typically, a principal resin is prepared by adducting an epoxy resin with
an amine. An aqueous electrodeposition coating bath is prepared by mixing
the principal resin with a crosslinking agent and salting it with acid and
deionized water to form a dispersion, mixing the dispersion with a pigment
paste and optionally with other additives like solvents, antifoam and the
like.
Pigment pastes are usually prepared by dispersing a pigment in a grinding
resin in the presence of plasticizers, wetting agents, surfactants or
other ingredients in a ball mill, sand mill, cowles mill or continuous
mill until the pigment has been reduced to the desired particle size and
is wetted by the resin or dispersed in it.
One disadvantage of pigment pastes is that they contain volatile organic
compounds (VOC).
It is therefore an object of the present invention to provide a process for
the preparation of a pigment dispersant for a cathodic electrocoating
composition which does not need the use of volatile organic compounds and
which provides stable aqueous pigment pastes or pigment dispersions.
Another object of the invention is an aqueous cathodic electrocoating
composition.
SUMMARY OF THE INVENTION
The objects of the present invention are achieved with a process for the
preparation of amine modified copolymers as pigment dispersants for
cathodic electrocoating compositions comprising the steps of
a) polymerizing
i) an ethylenically unsaturated monomer containing an isocyanate group with
ii) other ethylenically unsaturated monomers having no functional group
capable of undergoing a reaction with said isocyanate group to form a
copolymer with isocyanate groups and
b) reacting stepwise or simultaneously said isocyanate groups with
iii) a compound selected from the group consisting of a polyalkyleneglycol
monoalkyl ether, an aminoterminated polyalkylene glycol monoalkyl ether
and mixtures thereof and
iv) a compound containing at least a tertiary amino group and one
functional group capable of undergoing a reaction with said isocyanate
group and
v) optionally, another compound having one functional group capable of
undergoing a reaction with said isocyanate group.
DETAILED DESCRIPTION OF THE INVENTION
In step (a) of the process of the present invention, a copolymer with
isocyanate groups is formed by polymerizing
i) from about 5 to about 50% by weight, preferably from about 20 to about
30% by weight of an ethylenically unsaturated monomer containing an
isocyanate group with
ii) from about 50 to about 95% by weight, preferably from about 70 to about
80% by weight of another ethylenically unsaturated monomer having no
functional group capable of undergoing a reaction with said isocyanate
group.
Suitable ethylenically unsaturated monomers containing an isocyanate group
(i) comprise dimethyl-meta-isopropenyl benzyl isocyanate, vinylisocyanate,
isocyanatoethyl(meth)acrylate, isopropenyl isocyanate and mixtures
thereof. Preferred is dimethyl-meta-isopropyl benzyl isocyanate.
Ethylenically unsaturated monomers (ii) are suitable if they have no
functional group capable of undergoing a reaction with said isocyanate
group of monomers (i). These monomers may be chosen from acrylic or
methacrylic alkyl, aryl, aralkyl, alkoxyalkyl or aryloxyalkyl esters
derived from alcohols or phenols having to about 20 carbon atoms, or vinyl
monomers. The expression (meth)acrylate with parentheses as used herein
includes methacrylate and acrylate. Suitable examples are methyl
(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl
(meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate,
cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, phenyl
(meth)acrylate, para-tolyl (meth)acrylate, phenyethyl (meth)acrylate,
3-phenylpropyl (meth)acrylate, ethoxyethyl (meth)acrylate, phenoxyethyl
(meth)acrylate, and mixtures thereof. Also suitable are maleic acid and
fumaric acid dialkyl esters in which the alkyl groups have 1 to 20 carbon
atoms. Other suitable monomers are vinyl aromatics such as styrene,
alphamethyl styrene and vinyl toluene, halogenated vinyl benzenes such as
chlorostyrene, and other vinyl monomers such as vinyl chloride,
(meth)acrylamide and N-alkyl and N-aryl substituted (meth)acrylamides,
(meth)acrylonitrile, N-alkyl maleimides, N-aryl maleimides, and acrolein.
Preferred are styrene, phenyl(meth)acrylate, N-butyl (meth)acrylate,
cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate and
(meth)acrylonitrile.
Copolymerization is carried out using conventional techniques such as
heating the monomers in the presence of a polymerization initiating agent
and optionally chain transfer agents. The copolymerization may be carried
out in bulk or solution. For the present invention it is preferred to have
some solvent present to act as a cosolvent during dispersion. Solvents for
solution polymerization should not have functional groups capable to react
with the isocyanate groups of component (i).
Suitable solvents comprise ketones, such as methyl ethyl ketone, methyl
propyl ketone and acetone; esters, such as butyl acetate and pentyl
propionate; ethers, such as diethylene glycol dimethyl ether, dioxane,
tetrahydrofuran; N-methyl pyrrolidone, ketoesters, aromatic hydrocarbons,
alkanes, cyclic alkanes, and mixtures thereof.
Preferred solvents are ketones such as methyl ethyl ketone, methyl propyl
ketone, and methyl isobutyl ketone methyl amyl ketone and mixtures
thereof.
Typically initiators are peroxides such as dialkyl peroxides, peroxyesters,
peroxydicarbonates, diacyl peroxides, hydroperoxides, and peroxyketals and
azo compounds such as 2,2'-azobis(2-methylbutanenitrile) and 1,1'-azobis
(cyclohexanecarbonitrile).
Typical chain transfer agents are mercaptans such as octyl mercaptan, n- or
tert.-dodecyl mercaptan; halogenated compounds; thiosalicylic acid,
mercaptoacetic acid, mercaptoethanol, buten-1-ol, and dimeric alpha-methyl
styrene. Mercaptans are preferred.
The reaction is usually carried out at temperatures from about 20.degree.
C. to about 200.degree. C. The reaction may conveniently be done at the
temperature at which the solvent or solvent mixture refluxes, although
with proper control a temperature below the reflux may be maintained. The
initiator should be chosen to match the temperature at which the reaction
is carried out, so that the half-life of the initiator at that temperature
should preferably be between one minute and thirty minutes.
The solvent or solvent mixture is generally heated to the reaction
temperature and the monomer and initiator(s) are added at a controlled
rate over a period of time, usually between 2 and 6 hours. A chain
transfer agent or additional solvent may be fed in also at a controlled
rate during this time. The temperature of the mixture is then maintained
for a period of time to complete the reaction. Optionally, additional
initiator may be added to ensure complete conversion.
The NCO number of the copolymer is from about 0.3 meqg NV to 2.0 meqg NV,
preferably from about 0.9 meqg NV to about 1.5 meqg NV.
The copolymers of step (a) have a weight average molecular weight
determined by GPC versus polystyrene standards of from about 3,000 to
about 25,000, preferably from about 4,000 to about 10,000.
In step (b) the isocyanate groups of the copolymer of step (a) are reacted
stepwise or simultaneously with (iii) a polyalkylene glycol monoalkyl
ether or an amine-terminated polyalkylene glycol monoalkyl ether, (iv) a
compound containing at least one tertiary amino group and one functional
group capable of undergoing a reaction with said isocyanate group and (v)
optionally another compound having one functional group capable of
undergoing a reaction with said isocyanate group.
The polyalkylene glycol monoalkyl ether (iii) is preferably formed from
monoalcohol initiated polymerization of ethylene oxide, propylene oxide
and mixtures thereof with up to 30% by weight propylene oxide. Starting
monoalcohols are C.sub.1 -C.sub.18 alcohols like metnanol, ethanol,
n-propanol, i-propanol hexanol, decanol, undercanol and etheralcohols like
methoxyethanol, butoxyethanol and the like.
The amine-terminated polyalkylene glycol monoalkylether is preferably
formed from the amination of polyalkylene glycol monoalkyl ether.
The polyalkylene glycol monoalkyl ethers have molecular weights of from 300
to 20,000, preferably 1,000 to 2,500.
Preferred is polyethylene glycol monomethyl-ether.
Suitable compounds (iv) contain at least one tertiary amino group and one
functional group capable of undergoing a reaction with the isocyanate
group of the copolymer of step (a).
Examples of these compounds are alkanolamines containing at least one
tertiary amino group and one hydroxyl group like N,N dimethyl
ethanolamine, N,N diethyl ethanolamine, N,N dimethyl
propanolamine,N-hydroxyethylpiperidine, N-hydroxyethylpyrrolidine and the
like. Another group are amines containing at least one tertiary amino
group and one primary or secondary amino group like N,N dimethyl
propanediamine, N,N dimethyl ethanediamine, N,N dimethyl hexanediamine,
N-methyl piperazine, aminoethylmorpholine and aminoethylpiperidine.
Other suitable compounds comprise hydroxyethylpyridine and
aminoethylpyridine.
Preferred are N,N-dimethylpropanediamine and N,N-dimethylethanolamine.
Examples of compounds (v) are C.sub.1 -C.sub.36 mono or dialkyl amines such
as ethylamine, n-propylamine, i-propylamine, n-hexylamine,
2-ethylhexylamine, n-decylamine, stearylamine, diethylamine, dihexylamine,
distearylamine, N-methyl-N-ethylamine; C.sub.4 -C.sub.18 a mono or
dicycloaklylamines such as cyclopentylamine, cyclohexylamine,
dicyclohexylamine; heterocyclic C.sub.4 -C.sub.18 amines such as
pyrrolidine, piperidine and morpholine, aromatic C.sub.6 -C.sub.18 amines
such as aniline, p-toluidine, o-toluidine, diphenylamine, indole and
indoline; araliphatic C.sub.7 -C.sub.18 amines like benzylamine,
dibenzylamine, 2-phenylethylamine; C.sub.2 -C.sub.36 mono- and
di-alkanolamines like ethanolamine, diethanolamine, i-propanolamine,
h-hexanolamine, h-undecandamine, 3-aminopropanol, aminocyclohexanol and
2-(2-aminoethoxy)ethanol; C.sub.1 -C.sub.36 alcohols such as methanol,
ethanol, propanol, i-propanol, n-butanol, isobutanol, n-hexanol,
cyclohexanol, 2-ethylhexanol; C.sub.3 -C.sub.36 ether alcohols such as
methoxyethanol, butoxyethanol, 1-butoxy-2-propanol, and
(butoxyethoxy)ethanol.
Preferred are mono- and di- alkanolamines, particularly ethanolamine,
diethanolamine, and 3-aminopropanol.
As stated above, the components (iv) and (v) may be reacted one after
another or simultaneously with the isocyante groups of the copolymer of
step (a). Preferred is the stepwise reaction of first component (iv) and
second component (v).
The reaction is usually carried out at temperatures from about 20.degree.
C. to 150.degree. C., preferably from about 50.degree. C. to about
130.degree. C.
The molar ratio of the hydrogen functionality of component (iv) and (v) to
the isocyanate group of the copolymer of step (a) is from about 0.8 to
about 1.3, preferably from about 1.0 to about 1.3.
The reaction may be carried out in the presence of the same organic
solvents which have been used in step (a) and in the presence of a
catalyst such as organic tin compounds and/or tertiary amine.
The final amine modified copolymers have a weight average molecular weight
of from about 4,000 to about 30,000, preferably from about 5,000 to about
12,000.
For the preparation of the pigment paste, the pigments or dyestuffs are
dispersed in a solution of the copolymer in water with optional cosolvent
and ground in a ball mill, sand mill, cowles mill, attritor, or continuous
mill.
Examples of the dye stuffs or pigments may be inorganic or organic, for
example, graphite, carbon black, zinc chromate, strontium chromate, barium
chromate, lead chromate, lead cyanide, titanium dioxide, zinc oxide, iron
oxide, cadmium sulfide, iron oxide, aluminum flakes, mica flakes, zinc
sulfide, phthalocyanine complexes, naphthol red, carbazole violet,
perylene reds, quinacridones and halogenated thioindigo pigments, among
others.
The pigment paste has a concentration of from about 10 to about 60% by
weight, the optimum concentration of which depends on pigment type and
particle size.
The pigment paste of the present invention is added to an aqueous cathodic
electrocoating composition comprising a principal resin, which has been
solubilized by an acid, a crosslinker and additives in a known manner.
The concentration of the pigment paste is from about 1 to about 10% by
weight, preferably from about 2 to about 5% by weight, based on the total
weight of the aqueous cathodic electrocoating composition.
The principle resin is known in the art and described for example in U.S.
Pat Nos. 4,575,523; 4,661,541 and 4,780,524. It constitutes a
self-addition aromatic or alkyl aromatic epoxy resin with at least one
epoxy group with at least one amine with at least one primary or secondary
amino group. A particularly useful class of polyepoxides are the glycidyl
polyethers of polyhydric phenols like glycidyl polyethers of bisphenol A
having epoxide equivalent weights of from about 450 to about 2,000, more
typically from about 800 to about 1.600, and preferably from about 800 to
about 1,500.
Typical preferred commercial formulations of diglycidyl ether starting
materials are sold under the trade names "EPON 828" and "EPON 1001" (Shell
Chemical Co., Division of Shell Oil Company, 50 West 50th Street, New
York, N.Y.), Araldite GY 2600 (CibaGeigy, Division of Ciba Corporation,
Fair Lawn, N.J.), or DER 632 (Dow Chemical Co., Midland, Mich.).
Examples of amines with at least one primary or secondary amine group
include aliphatic diamines and triamines, aliphatic alcohol amines,
alkylene diamines, alkanol amines and N-alkyl substituted forms thereof.
Especially preferred are the aliphatic diamines and alcohol amines having
1 to 10 carbons in the aliphatic group.
Examples for diamines are ethylene diamine, 1,2-propylene diamine,
1,3-propylene diamine, 1,2-butylene diamine, 1,3-butylene diamine,
1,4-butylene diamine, 1,5-pentalene diamine, 1,6-hexylene diamine,
1,4-diaminocyclohexane, methyl-aminopropylamine,
N,N-dimethylaminopropylamine and the like.
Examples for aminoalcohols are ethanolamine, diethanolamine and
N-methylethanolamine.
Preferred examples are N,N-dimethylaminopropyl amine, ethanolamine,
diethanolamine and N-methylethanolamine.
In the principal resin, the amine adducted to the self-addition diepoxide
produces terminal amine groups. These provide the cationic sites which
largely contribute to the ready dispersibility of the principal resin in
the aqueous acidic medium. The equivalent ratio of amine mixture per
epoxide group of the self-addition diepoxide is from 0.75 to 1, primary
and secondary amines being counted as one equivalent each.
The reaction conditions are known and typically, the reaction temperature
will be about 20.degree. C. to about 100.degree. C., more typically about
30.degree. C. to about 80.degree. C., and preferably about 60.degree. C.
to about 75.degree. C. The reaction time is typically about five minutes
to about 60 minutes, more typically about ten minutes to about 40 minutes
and preferably about 25 minutes to about 30 minutes.
The preferred crosslinker used in the practice of this invention are the
organic polyisocyanates and, in particular, the blocked polyisocyanates.
The organic polyisocyanates and the blocking agents used in the practice
of this invention are typical of those used in the art, e.g., U.S. Pat.
No. 4,182,831 the disclosure of which is incorporated by reference.
Useful blocked polyisocyanates are those which are stable in the dispersion
systems at ordinary room temperature and which react with the resinous
product of this invention at elevated temperatures.
In the preparation of the blocked organic polyisocyanates, and suitable
organic polyisocyanate can be used. Representative examples are the
aliphatic compounds such as trimethylene, tetramethylene, pentamethylene,
hexamethylene, 1,2-propylene, 1,2-butylene, 2,3-butylene and 1,3-butylene
diisocyanates; the aromatic compounds such as m-phenylene, p-phenylene,
4,4'-diphenyl, and 1,4-napthalene diisocyanates; and aliphatic aromatic
compounds such as 4,4'-diphenylene methane, 2,4- or 2,6-tolylene, or
mixtures thereof, 4,4'-toluidine, and 1,4-xylylene diisocyanates; and
triisocyanates such as triphenyl methane -4,4',4"-triisocyanate,
1,3,5-triisocyanate benzene and 2,4,6-triisocyanate toluene and the
tetraisocyanates such as 4,4'-diphenyl-dimethyl methane-2,2',
5,5'tetraisocyanate; the polymerized polyisocyanates such as tolylene
diisocyanate dimers and trimers, polymethylenepolyphenylene
polyisocyanates having NCO functionalities of 2 to 3, and the like.
In addition, the organic polyisocyanate can be a prepolymer derived from a
polyol such as glycols, e.g., ethylene glycol and propylene glycol, as
well as other polyols such as glycerol, trimethylolpropane, hexanetriol,
pentaerythritol, and the like as well as monoethers, such as diethylene
glycol, tripropylene glycol and the like and polyethers, i.e., alkylene
oxide condensates of the above. Among the alkylene oxides that may be
condensed with these polyols to form polyethers are ethylene oxide,
propylene oxide, butylene oxide, styrene oxide and the like. These are
generally called hydroxyl-terminated polyethers and can be linear or
branched. Especially useful polyether polyols are those derived from
reacting polyols such as ethylene glycol, diethylene glycol, triethylene
glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,6-hexanediol, and
their mixtures; glycerol trimethylolethane, trimethylolpropane,
1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, tripentaerythritol,
polypentaerythritol, sorbitol, methyl glucosides, sucrose and the like
with alkylene oxides such as ethylene oxide, propylene oxide, their
mixtures, and the like.
Preferred polyisocyanates include the reaction product of toluene
diisocyanate and trimethylolpropane, the reaction product of
4,4'-diphenylene methane diisocyanate and trimethylolpropane, and
4,4'-diphenylene methane diisocyanate with glycerol; additionally, the
isocyanurate of hexamethylene diisocyanate.
Any suitable aliphatic, cycloaliphatic, aromatic, alkyl monoalcohol and
phenolic compound can be used as a blocking agent in the practice of the
present invention, such as lower aliphatic alcohols, such as methyl,
ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl, nonyl,
3,3,5-trimethyl-hexanol, decyl and lauryl alcohols, and the like; the
aromatic-alkyl alcohols, such as phenylcarbinol, methylphenylcarbinol,
ethyl glycol monoethyl ether, ethyl glycol monobutyl ether and the like;
the phenolic compounds such as phenol itself, substituted phenols in which
the substituents do not adversely affect the coating operations. Examples
include cresol, nitrophenol, chlorophenol and t-butyl phenol.
Also, amines can be used as blocking agent like dibutylamine.
A preferred blocking agent is monopropyl ether of ethylene glycols.
Additional blocking agents include tertiary hydroxyl amines, such as
diethylethanolamine and oximes, such as methylethyl ketoxime, acetone
oxime and cyclohexanone oxime, and caprolactam. A preferred oxime is
methyl-n-amyl ketoxime.
The blocked polyisocyanates are formed by reacting sufficient quantities of
blocking agent with sufficient quantities of organic polyisocyanate under
reaction conditions conventional in this art such that no free isocyanate
groups are present when the reaction has run its course.
Sufficient quantities of blocked polyisocyanate are incorporated into the
electrodepositable coating compositions of this invention such that the
deposited coating will be completely cured upon baking and there will be
no free isocyanate groups remaining. Typically, about 20% by weight to
about 80% by weight of blocked polyisocyanate is mixed with the modified
epoxy resin, more typically about 30% by weight to about 70% by weight,
preferably about 35% by weight to about 65% by weight.
Additives may be used like organic solvents, catalysts, wetting agents,
conditioning agents, thickeners, rheology control agents, antioxidants,
surfactants, leveling agents, or mixtures thereof.
Electrodepositable cathodic coating compositions of this invention are used
in an electrodeposition process as an aqueous dispersion. Sufficient
quantities of the components are used so that the concentration of the
components in an aqueous bath will produce a coating on an object of
sufficient thickness when processed at a sufficient voltage, time and
temperature so that upon baking the coating will have the desired
characteristics such as filmbuild, throwpower, corrosion resistance, chip
resistance, impact resistance. Typically, the concentration in water of
the components of this invention are 10% by weight to about 60% by weight,
typically about 20% by weight to about 60% by weight, and preferably about
30% by weight to about 60% by weight.
The electrodeposition process typically takes place in an electrically
insulated tank containing an electrically conductive anode which is
attached to a direct current source. The size of the tank will depend on
the size of the article to be coated. Typically the tank is constructed of
stainless steel or mild steel lined with a dielectric coating such as
epoxy impregnated fiberglass or polyepoxide. The electrodepositable
cathodic resinous coating compositions of this invention are typically
used to coat articles such as automobile or truck bodies. The typical size
of an electrodeposition bath tank used for this purpose is about 60,000
gallons to about 120,000 gallons capacity.
Typically the article to be coated is connected to the direct current
electric circuit so that the conductive object acts as the cathode. When
the article is then immersed in the coating bath, flow of electrons from
the cathode to the anode, that is, conventional current flow from the
anode to the cathode, results in the particles of the dispersed cationic
electrodepositable resin composition being deposited on the surfaces of
the article. The particles of the dispersed resin composition are
positively charged and are therefore attracted to the negative cathodic
surface of the object to be coated. The thickness of coating deposited
upon the object during its residence in the electric cathodic coating bath
is a function of the cathodic electrodepositable resin composition, the
voltage across the article, the current flux, the pH of the coating bath,
the conductivity, and the residence time. Sufficient voltage is applied to
the coated article for a sufficient time to obtain a coating of sufficient
thickness. Typically the voltage applied across the coated article is
about 50 volts to about 500 volts, more typically about 200 to about 350
volts, and preferably about 225 volts to about 300 volts. The current
density is typically about 0.5 amperes per sq. ft. to about 30 amperes per
sq. ft., more typically about one ampere per sq. ft. to about 25 amperes
per sq. ft., and preferably about one ampere per sq. ft. The article to be
coated typically remains in the coating bath for a sufficient period of
time to produce a coating or film of sufficient thickness having
sufficient resistance to corrosion and flexibility. The residence time or
holding time is typically about 1 minute to about 21/2 minutes, and
preferably about 2 minutes.
The pH of the coating bath is sufficient to produce a coating which will
not rupture under the applied voltage. That is, sufficient pH to maintain
the stability of the coating bath so that the resin does not kick-out of
the dispersed state and to control the conductivity of the bath. Typically
the pH is about 4 to about 7, more typically about 5 to about 6.8, and
preferably about 6 to about 6.5.
The conductivity of the coating bath will be sufficient to produce a coated
film of sufficient thickness.
The desirable coatings have sufficient thicknesses to provide resistance to
corrosion while having adequate flexibility. Typically, the film
thicknesses of the coated objects of this invention will be about 0.4 mils
to about 1.8 mils, more typically about 0.6 mils to about 1.6 mils, and
preferably about 0.6 mils to about 1.0 mils.
The temperature of the coating bath is maintained, typically by cooling, at
a temperature less than about 30.degree. C.
When the desired thickness of the coating has been produced, the coated
object is removed from the electrodeposition bath and cured. Typically,
the electrodeposited coatings are cured in a conventional convection oven
at a sufficient temperature for a sufficient length of time to cause the
cross-linking composition to cross-link the resin. In the case of a
blocked polyixocyanate, this would be a sufficient time and temperature to
unblock the blocked polyisocyanates and allow for cross-linking of the
electrodepositable resin compositions. Typically, the coated articles will
be baked at a temperature of about 85.C. to about 290.degree. C., more
typically about 110.degree. C. to about 170.degree. C., and preferably
about 120.degree. C. to about 160.degree. C. The coated articles will be
baked for a time period of about ten minutes to about 40 minutes, more
typically about ten minutes to about 35 minutes, and preferably about 15
minutes to about 30 minutes.
It is contemplated that the coated articles of the present invention may
also be cured by using radiation, vapor curing, contact with heat transfer
fluids and equivalent methods.
Typically, the coated articles of this invention will comprise conductive
substrates such as metal, including steel, aluminum, copper, etc.;
however, any conductive substrate having a conductivity similar to the
aforementioned metals may be used. The articles to be coated may comprise
any shape so long as all surfaces can be wetted by the electrodeposition
bath. The characteristics of the article to be coated, which have an
effect on the coating, include the shape of the article, the capacity of
the surfaces to be wetted by the coating solution, and the degree of
shielding from the anode. Shielding is defined as the degree of
interference with the electromotive field produced between the cathode and
the anode, thereby preventing coating composition from being deposited in
those shielded areas. A measure of the ability of the coating bath to coat
remote areas of the object is throwpower. Throwpower is a function of the
electrical configuration of the anode and cathode as well as the
conductivity of the electrodeposition bath.
The invention provides good pigment pastes or pigment dispersions, less
pigment settling characteristics in the electrocoat bath, a reduced amount
of the total pigment, and a low VOC-coating. The coating of the coated
article exhibit good appearance, hiding, gloss, film thickness, chip
impact corrosion resistance and intercoat adhesion.
EXAMPLES
Example 1
Preparation of Isocyanate Functional Acrylic Copolymer 1
427.8 g (4.97 mol) of methyl propyl ketone was charged to a reaction vessel
fitted with stirrer and condensor. The vessel was heated to reflux
temperature and maintained at reflux for the duration of the reaction. A
blend consisting of 495.0 g (4.41 mol) styrene, 405.6 g (2.85 mol) butyl
methacrylate, and 382.6 g (1.90 mol) 1-(1-isocyanato-1-methyl
ethyl)-3-(1-methyl ethenyl)benzene, hereafter referred to as TMI, was
slowly added over a period of three hours. 64.1 g of tert-butyl peroctoate
was added to the monomer blend to initiate the vinyl polymerization. 32.2
g of initiator along with 123.0 g of methyl propyl ketone were added one
half hour after the addition of monomer was complete. The mixture was
heated for an additional 1.5 hours and then cooled and collected for
further modification.
Example 2
Preparation of Isocyanate Functional Acrylic Copolymer 2
231.3 g (2.03 mol) of methyl amyl ketone was charged to a reaction vessel
fitted with stirrer and condensor. The vessel was heated to reflux
temperature and maintained at reflux for the duration of the reaction. A
blend consisting of 94.8 g (0.91 mol) styrene, 160.7 g (1.13 mol) butyl
methacrylate, 144.8 g (1.13 mol) butyl acrylate, and 382.6 g (1.90 mol)
TMI, was slowly added over a period of three hours. 67.2 g of 50% active
tert-butyl peroxy acetate was added to the monomer blend to initiate the
vinyl polymerization. 33.6 g of 50% active initiator along with 55.0 g
methyl amyl ketone were added one half hour after the addition of monomer
was complete. The mixture was heated for an additional 1.5 hours and then
cooled and collected for further modification.
Example 3
Preparation of Isocyanate Functional Acrylic Copolymer 3
251.0 g (2.51 mol) of methyl amyl ketone was charged to a reaction vessel
fitted with stirrer and condensor. The vessel was heated to reflux
temperature and maintained at reflux for the duration of the reaction. A
blend consisting of 294.8 g (1.60 mol) 2-ethyl-hexyl acrylate, 269.2 g
(1.60 mol) cyclohexyl methacrylate, and 322.0 g (1.60 mol) TMI, was slowly
added over a period of three hours. 88.6 g of 50% active tert-butyl peroxy
acetate was added to the monomer blend to initiate the vinyl
polymerization. 44.3 g of 50% active initiator along with 62.2 g methyl
amyl ketone were added one half hour after the addition of monomer was
complete. The mixture was heated for an additional 1.5 hours and then
cooled and collected for further modification.
Example 4
Preparation of Modified Copolymer 1 (Grind Resin)
54.9 g (39.2 mmol; average molecular weight of 1400) of methoxy
polyethylene glycol in 12.9 g toluene and 111.2 g of the
isocyanate-functional acrylic prepared in accordance with Example 1 were
charged to a reaction vessel fitted with a stirrer and condensor. The
mixture was heated to reflux and maintained at reflux for not more than
one half hour. At the end of this time, the mixture was titrated and the
result indicated that all of the methoxy polyethylene glycol had reacted
with the isocyanate groups. The remainder of the isocyanate functionality
was reacted with 1.80 g (29.4 mmol) monoethanolamine and 3.00 g (29.4
mmol) dimethylaminopropylamine which was added while the mixture was
stirred and the temperature was approximately 36.degree. C. The
temperature then rose to 42.degree. C. and then subsided. When the
exothermic reaction had ceased, the mixture was titrated. Titration
revealed no remaining NCO functionality and the expected amount of amine
functionality. The material was subsequently dispersed with 8.8 g of
deionized water.
Example 5
Preparation of Modified Copolymer 2 (Grind Resin)
101.3 g (72.4 mmol; average molecular Weight of 1400) of methoxy
polyethylene glycol in 23.8 g toluene and 205.6 g of the
isocyanate-functional acrylic prepared in accordance with Example 1 were
charged to a reaction vessel fitted with a stirrer and condensor. The
mixture was heated to 90.degree. C. and maintained at 90.degree. C. for
three hours, after which time titration indicated that all of the methoxy
polyethylene glycol had reacted with the isocyanate groups. The reaction
mixture was cooled to around 40.degree. C. and 4.60 g (45.2 mmol)
3-(dimethylamino)propylamine and 5.5 g (27.2 mmol) 11-aminoundecanoic acid
were successively added to the mixture. The mixture was heated to reflux
and maintained at reflux for 15 minutes, after which time all the solid
material had dissolved. The reaction mixture was cooled to around
70.degree. C. degrees and the remainder of the isocyanate funtionality was
reacted with 2.20 g (27.2 mmol) monoethanolamine, then an additional 5.0 g
methyl propyl ketone was added to the mixture to decrease the viscosity.
Example 6
Black Pigment Paste 1
A black pigment paste was prepared by adding 18.19 parts by weight Raven
890H carbon black pigment (Columbian Chemicals Company, 1600 Parkwood
Circle, Atlanta, Ga. 30339) to a stirred mixture consisting of 2.59 parts
by weight grind resin prepared in accordance with Example 4, 72.00 parts
by weight deionized water, and 7.23 parts by weight ethylene glycol
monobutyl ether. The resultant mixture was stirred on cowles for about
thirty minutes and milled in an attritor for ninety minutes.
Example 7
Black Pigment Paste 2
A black pigment paste was prepared by adding 18.19 parts by weight Raven
410 carbon black pigment (Columbian Chemicals Company) to a stirred
mixture consisting of 2.59 parts by weight grind resin prepared in
accordance with Example 5, 72.00 parts by weight deionized water, and 7.23
parts by weight ethylene glycol monobutyl ether. The resultant mixture was
stirred on cowles for about thirty minutes and milled in an attritor for
two hours.
Example 8
Lead Silicate Pigment Paste
A lead silicate pigment paste was prepared by adding 18.19 parts by weight
Basic lead silicate 202 (Chemcentral Corporation, 7050 West 71st Street,
Chicago, Ill. 60638) to a stirred mixture consisting of 2.59 parts by
weight grind resin prepared in accordance with Example 5, 72.00 parts by
weight deionized water, and 7.23 parts by weight ethylene glycol monobutyl
ether. The resultant mixture was stirred on cowles for about thirty
minutes and milled in an attritor for two hours.
Example 9
Dibutyltin Oxide Paste
A dibutyltin oxide paste was prepared by adding 18.19 parts by
weight Fascat 4203 dibutyltin oxide catalyst (Atochem North America,
Incorporated, 3 Parkway, Philadelphia, Pa. 19102) to a stirred mixture
consisting of 2.59 parts by weight grind resin prepared in accordance with
Example 5, 72.00 parts by weight deionized water, and 7.23 parts by weight
ethylene glycol monobutyl ether. The resultant mixture was stirred on
cowles for about thirty minutes and milled in an attritor for two hours.
Example 10
Aluminum Silicate Extender Paste
An aluminum silicate extender paste was prepared by adding 18.19 parts by
weight ASP200 aluminum silicate extender (Engelhard Corporation, 101 Wood
Avenue, Iselin, N.J. 08830) to a stirred mixture consisting of 2.59 parts
by weight grind resin prepared in accordance with Example 5, 72.00 parts
by weight deionized water, and 7.23 parts by weight ethylene glycol
monobutyl ether. The resultant mixture was stirred on cowles for about
thirty minutes and milled in an attritor for two hours.
Example 11
Red pigment paste
A red pigment paste was prepared by adding 38.47 parts by weight
diketopyrrolopyrrole pigment (C. I. Pigment Red 254) to a stirred mixture
consisting of 2.20 parts by weight grind resin prepared in accordance with
Example 4, 54.00 parts by weight deionized water, and 5.33 parts by weight
ethylene glycol monobutyl ether. The resultant mixture was stirred on
cowles for about thirty minutes and milled in an attritor for sixty
minutes.
Example 12
Preparation of Electrocoating Bath 1 and Deposition of Films
A coating composition was prepared which contained the dispersant
stabilized carbon black pigment grind prepared in accordance with the
present invention above. 2592 parts by weight of principle emulsion
prepared in accordance with the teachings of U.S. Pat. No. 4,920,162 were
mixed with 1725 parts by weight deionized water. 82.5 parts by weight of
the black pigment paste prepared in accordance with Example 6 was added to
the mixture and the resulting bath was heated to 32.degree. C.
Electrodeposition of the coating films on zinc phosphated steel panels was
performed by immersion of the panels in the bath for about 2 minutes at a
voltage of 215V. The coated panels were rinsed, then baked at 180.degree.
C. for 20-30 minutes to harden the films.
Example 13
Preparation of Electrocoating Bath 2 and Deposition of Films
A coating composition was prepared which contained the dispersant
stabilized red pigment grind prepared in accordance with the present
invention above. 1485 parts by weight of principle emulsion prepared in
accordance with the teachings of U.S. Pat. No. 4,920,162 were mixed with
1154 parts by weight deionized water. 179 parts by weight of the red
pigment paste prepared in accordance with Example 11 and 41.1 parts by
weight of the dibutyltin oxide paste prepared in accordance with Example 9
were added to the mixture and the resulting bath was heated to 32.degree.
C. Electrodeposition of the coating films on zinc phosphated steel panels
was performed by immersion of the panels in the bath for about 2 minutes
at a voltage of 200 V. The coated panels were rinsed, then baked at
180.degree. C. for 20-30 minutes to harden the films.
Example 14
Preparation of Electrocoating Bath 3 and Deposition of Films
A coating composition was prepared which contained the dispersant
stabilized pigment grinds prepared in accordance with the present
invention above. 1215 parts by weight of principle emulsion prepared in
accordance with the teachings of U.S. Pat. No. 4,920,162 were mixed with
843.5 parts by weight deionized water. 38.1 parts by weight of the black
pigment paste prepared in accordance with Example 7, 27.5 parts by weight
of the lead silicate pigment paste prepared in accordance with Example 8,
38.9 parts by weight of the dibutyltin oxide paste prepared in accordance
with Example 9, and 357 parts by weight of the aluminum silicate extender
paste prepared in accordance with Example 10 were added to the mixture and
the resulting bath was heated to 32.degree. C. Electrodeposition of the
coating films on zinc phosphated or bare steel panels was performed by
immersion of the panels in the bath for about 2 minutes at a voltage of
215 V. The coated panels were rinsed, then baked at 180.degree. C. for
20-30 minutes to harden the films.
Example 15
Preparation of Electrocoating Bath 4 (Control) and Deposition of Films
A coating composition was prepared with the same pigment concentration as
in Example 14, but the pigment paste was prepared using a grind resin
prepared in accordance with the teachings of U.S. Pat. No. 4,920,162. 1945
parts by weight of principle emulsion prepared in accordance with the
teachings of U.S. Pat. No. 4,920,162 were mixed with 2073 parts by weight
deionized water. 382 parts by weight of a mixed pigment paste prepared in
accordance with the teachings of U.S. Pat. No. 4,920,162 and having the
same relative pigment concentrations as in Example 14 was added to the
mixture and the resulting bath was heated to 32.degree. C.
Electrodeposition of the coating films on zinc phosphated or bare steel
panels was performed by immersion of the panels in the bath for about 2
minutes at a voltage of 215 V. The coated panels were rinsed, then baked
at 180.degree. C. for 20-30 minutes to harden the films.
The bath of Example 12 prepared with carbon black as the sole pigment was
quite stable and showed no settling over a period of a week. Carbon black
will often show some settling or kick-out in baths prepared with pastes
using grind resins such as those described in U.S. Pat. Nos. 4,920,162,
4,780,524 and 4,661,541. This bath deposited to form a hardened film of 23
microns in thickness but was somewhat soft because of the lack of any
catalyst which would accelerate the curing reaction.
The bath of Example 13 prepared with C.I. Pigment Red 254 shows that the
present invention allows the introduction of organic pigments into a
cathodic electrocoat system. It is quite difficult to grind organic
pigments using grind resins such as those described in U.S. Pat. Nos.
4,920,162, 4,780,524 and 4,661,541. This bath deposited to form a cured
glossy film of 22 microns in thickness.
The use of the present invention also affords improvements in chip
resistance and scribe creep on bare steel. The results of tests run on
panels from Example 14 and Example 15 (control) are summarized below.
______________________________________
Example 14
Example 15
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Average Percent Paint Loss
0.65% 3.23%
1200 ml Shot Blast
Average Scribe Creep
8.49 mm 12.95 mm
Bare Steel
Average Scribe Creep
2.30 mm 2.21 mm
Zinc Phosphated Steel
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